The present invention relates to an improvement of a silent discharge type gas laser device.
Referring to FIGS. 1 to 4, the conventional gas laser device especially a transversal excitation type CO.sub.2 laser device will be illustrated.
FIG. 1 is a circuit of the conventional gas laser device in principle and FIG. 2 is a diagram of a system for a laser gas, and FIG. 3 is a sectional view of an electrode for the gas laser device.
In FIG. 1, the reference numeral (1) designates a grounded metallic electrode; (2) designates a high voltage side electrode and the discharging surface of the high voltage side electrode (2) is coated with a dielectric (3); (4) designates a discharging space; (5) designates a transformer; (6) designates a high frequency power source. The output terminal of the high frequency power source (6) is connected to an input winding of the transformer 5. One of the output terminals of transformer is grounded and the high voltage at the other terminal is applied to the high voltage side electrode (2).
The reference numeral (7) designates a full reflector; (8) designates an output side reflector (partially transmitting); (9) designates a coolant water recycling pump; (10) designates a coolant water vessel; (11) designates an ion exchange type pure water column which is connected to the grounded metallic electrode (1) and the high voltage type metallic electrode (2) and the full reflector (7) is connected to the coolant water recycling pump (9).
In FIG. 1, the silent discharge as stable discharge results in the discharging space (4) by applying an AC high voltage from the high frequency power source (6) and the transformer (5) to the high voltage side electrode (2). The silent discharge is the AC discharge given through the dielectric between the grounded metallic electrode (1) and the high voltage side electrode (2) and the non-equilibrium discharge which has high electron temperature but low molecular temperature can be made stable without changing to the arc discharge.
The light inducing radiation created by molecules excited in the discharging space (4) is not described in detail. Thus, the laser oscillation results in a resonator comprising the full reflector (7) and the output side reflector (8) by the silent discharge in the discharging space (4) whereby the laser is radiated from the output side reflector (8). Both the grounded metallic electrode (1) and the high voltage side electrode (2) are cooled with a coolant water having low electric conductivity and the coolant water is recycled through the coolant water vessel (10) and the ion exchanger type pure water column (11) by the coolant water recycling pump (9). The ion exchanger type pure water column (11) is required to reduce the electric conductivity of the coolant water and to prevent current leakage from the high voltage side electrode (2).
FIG. 2 is a diagram of a system for the laser gas. In FIG. 2, the reference numeral (12) designates a blower and (13) designates a heat exchanger. The temperature of the laser gas is lowered by the heat exchanger (13) with the coolant water (14) and the speed of the laser gas is accelerated by the blower (12) and the laser gas having high speed is passed through the discharging space (4) perpendicularly to the discharge and the laser light. The speed of the laser gas in the discharging space (4) is at a high speed of about 30 ms.sup.-1 whereby the excited molecules are uniformly distributed to the down flow side (5 to 2 mm) and elevation of the temperature of the laser gas caused by heat energy given by the discharge is suppressed. The CO.sub.2 laser absorbance is rapidly increased by the elevation of the temperature of the laser gas whereby the energy efficiency of the laser oscillation is lowered. Accordingly, said feature is important for lowering the elevation of the temperature of the laser gas.
FIG. 3 is an enlarged sectional view of the grounded metallic electrode (1) and the high voltage side electrode (2).
FIG. 4 is a sectional view taken along the line IV--IV of FIG. 3.
As it is clear from FIGS. 3 and 4, the discharging surfaces of both of the grounded metallic electrode (1) and the high voltage side electrode (2) are parallel flat planes whereby discharge uniformly results between the electrodes as shown in FIGS. 3 and 4.
In order to achieve laser oscillation, it is necessary to have laser gain for overcoming the losses by the full reflector (7) and the output side reflector (8) in the discharging space (4).
The laser gain is decided depending upon a length of the discharging space (4) in the optical axis and a discharge power density (discharge power per unit area). When the length of the discharging space in the optical axis is constant, laser oscillation does not results if the discharge power density is lower than the specific value.
In order to increase the discharge power density, either the frequency of the power source is increased or the applied voltage is increased or the electrostatic capacity of the dielectric is increased. The increase of applied voltage is limited because of the terminal insulation, and the electrostatic capacity of the dielectric is also limited because of the insulation durability and the dielectric constant of the material. Accordingly, it is necessary to use a higher frequency for increasing the discharge power density. Thus, the power frequency should be in a range of several tens KHz to 100 KHz.
The conventional silent discharge type laser device has the disadvantage of a higher power frequency. The higher power frequency causes higher cost of the high frequency power source (6) and greater power loss caused by the frequency conversion.
Accordingly, it is remarkably practical advantage to decrease the power frequency.